PAF-like lipids- and PAF-induced gallbladder muscle contraction is mediated by different pathways in guinea pigs

Human colonic myogenic dysfunction induced by mucosal lipopolysaccharide translocation and oxidative stress

BACKGROUND

Impairment of gastrointestinal motility is frequently observed in patients with severe infection.

AIM

To assess whether exposure of human colonic mucosa to pathogenic lipopolysaccharide affects smooth muscle contractility.

METHODS

Human colonic mucosa and submucosa were sealed between two chambers, with the luminal side facing upwards and covered with Krebs solution, with or without lipopolysaccharide from a pathogenic strain of Escherichia coli (O111:B4; 1,000 ng/mL), and with the submucosal side facing downwards into Krebs. The solution on the submucosal side was collected following 30-min mucosal exposure to Krebs without (N-undernatant) or with lipopolysaccharide (lipopolysaccharide undernatant). Undernatants were tested for lipopolysaccharide and hydrogen peroxide levels and for their effects on smooth muscle cells in the presence of catalase, indomethacin or MG132.

RESULTS

Smooth muscle cells incubated with N-undernatant had a maximal contraction of 32 ± 5% that was reduced by 62.9 ± 12% when exposed to lipopolysaccharide undernatant. Inhibition of contraction was reversed by catalase, indomethacin and MG132. Lipopolysaccharide levels were higher in the lipopolysaccharide undernatant (2.7 ± 0.7 ng/mL) than in N-undernatant (0.45 ± 0.06 ng/mL) as well as hydrogen peroxide levels (133.75 ± 15.9 vs 82 ± 7.5 nM respectively).

CONCLUSIONS

Acute exposure of colonic mucosa to pathogenic lipopolysaccharide impairs muscle cell contractility owing to both lipopolysaccharide mucosal translocation and production of free radicals.

Progesterone receptor A mediates VIP inhibition of contraction

The slow transit time of the colon in females with constipation is due to impairment of agonist-induced contraction. The impairment is associated with downregulation of G proteins that mediate contraction and upregulation of Gs proteins that mediate relaxation. These changes are caused by overexpression of progesterone (P4) receptors in the colon, rendering its muscle cells sensitive to physiological P4 concentrations. Downregulation of Gq/11 is mediated by P4 receptor B (PR-B). We examined whether upregulation of Gs proteins increased the inhibition of contraction and whether the increase is mediated by the P4 receptor A (PR-A). These studies were conducted in colon-isolated colon muscle cells from human control and slow-transit constipation (STC) females and from guinea pigs. Muscle cell contraction was induced by CCK-8. Inhibition of contraction was induced by vasoactive intestinal polypeptide (VIP), and 8'bromo-c'AMP (8B-c'AMP) G protein levels were determined by Western blot. VIP-induced inhibition of contraction was greater in muscle cells from STC and P4-treated muscle cells. There were no differences in the inhibition induced by 8B-c'AMP between muscle cells from STC and P4-treated controls. The increased VIP-induced inhibition of muscle cells treated with P4 was blocked by pretreatment with PR-A antibodies and unaffected by PR-B antibodies. These antibodies had no effect on 8B-c'AMP induced-inhibition. The P4 upregulation of Gs proteins was blocked by PR-A antibodies and unaffected by PR-B antibodies. Similar results were obtained in muscle cells from guinea pig colons. We concluded that P4 upregulation of Gs proteins increases VIP-induced inhibition of contraction mediated by PR-A.

Effects of progesterone on motility and prostaglandin levels in the distal guinea pig colon

Progesterone (P4) inhibits the gastrointestinal muscle contraction by downregulating Galpha(q/11) proteins that mediate contraction, by upregulating Galpha(s) proteins that mediate relaxation, and by altering the pattern of cyclooxygenase (COX) enzymes and prostaglandins. We aimed to examine whether P4 treatment of guinea pigs in vivo affects basal colon motility [basal motility index (MI)] by altering the levels and actions of PGF(2alpha) and PGE(2). Guinea pigs were treated with intramuscular (IM) P4 for 4 days. The BASAL MI, the PGF(2alpha)-induced contraction, and PGE(2)-induced inhibition of contraction were examined in muscle strips and cells. The levels of PGF(2alpha) and PGE(2) were measured by radioimmunoassay. Treatment with P4 reduced the basal MI, the levels of PGF(2alpha), and PGF(2alpha)-induced contraction. P4 increased PGE(2) levels, and PGE(2) induced relaxation. Pretreatment with IM RU-486 (10 mg/kg per day), a P4 receptor antagonist, 1 h before P4 blocked the actions of P4. The PGF(2alpha) antagonist Al-1180 abolished basal MI and PGF(2alpha)-induced contraction. N-ethylmaleimide, which blocks unoccupied membrane receptors, blocked Ach and VIP actions but had no effect on PGF(2alpha) and PGE(2) effects. A COX-1 inhibitor decreased and a COX-2 inhibitor increased PGF(2alpha) levels; GTPgammaS increased and GDPbetaS decreased the levels of PGF(2alpha). Galpha(q/11) protein antibodies (Abs) reduced PGF(2alpha) levels, and Galpha(i3) Abs blocked its motor actions. Galphas Abs increased PGF(2alpha) but decreased PGE(2) levels. We concluded that P4 decreases basal MI by reducing PGF(2alpha) levels caused by downregulation of Galpha(q/11) and that PGF(2alpha)-induced contraction was blocked by downregulating Galpha(i3). P4 also decreased the basal MI by increasing PGE(2) levels, and PGE(2) induced relaxation by upregulating Galpha(s) proteins.

Contribution of Rho-kinase in human gallbladder contractions

Rho/Rho-kinase-mediated pathway has been involved in a variety of physiological processes, including Ca2+ sensitization, which enhances smooth muscle contraction. In this study, first of all we investigated the expression of Rho-kinase (ROCK-2) and then the role of this protein in the control of smooth muscle contraction in the isolated human gallbladder. For this purpose, we examined the effects of a selective Rho-kinase inhibitor, (+)- (R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632, 10(-8)-3x10(-5) M) on carbachol (10(-8)-10(-4) M), cholecystokinin-8 (10(-8) M), endothelin-1 (10(-8) M), histamine (10(-5) M), neurokinin A (10(-7)-10(-6) M), 5-hydroxytryptamine (10(-6)-10(-5) M) and potassium chloride (KCl, 25-50 mM)-induced contractions as well as spontaneous contractile activity. Y-27632 (10(-5) M) significantly reduced 5-hydroxytryptamine, neurokinin A and KCl-induced contractions. Moreover, this Rho-kinase inhibitor (10(-8)-3x10(-5) M, cumulatively) relaxed the contractions produced by cholecystokinin-8, endothelin-1 and histamine in a concentration-dependent manner, being the pEC50 values for Y-27632 5.74+/-0.12, 5.33+/-0.09 and 5.95+/-0.18, respectively. Carbachol (10(-8)-10(-4) M) produced concentration-dependent contractions, which were also inhibited significantly by Y-27632. In addition, the spontaneous contractile activity was suppressed in the presence of Y-27632 (10(-6)-10(-5) M). Moreover, Western blot analysis has revealed that Rho-kinase is expressed in homogenates of the human gallbladder. Taken together, these results show that Rho-kinase is expressed in the human gallbladder, and it has an essential role in agonists and depolarization-induced contractions as well as spontaneous contractile activity.